OBJECTIVE: The objectives are 1) to determine whether Sr and F alone and in combination speeds up the remineralization of enamel white spots and 2) to test the rate of demineralization and remineralization of enamel with and without Sr and F, alone and in combinations, 3) to determine the effect, distribution and rate of change of ions (Ca and P or Sr and F when involved) within a diffusion barrier and the underlying dental enamel during demineralization and remineralization and 4) to determine whether the remineralized enamel has acquired added resistance to an acid challenge. METHODS: Known areas on extracted human teeth (patients' age: 12-14 years) will be covered with four layers of thin, inert mesh, and an artificial plaque will be gelled into the meshes. The areas will be subjected to a demineralizing solution, a remineralizing solution and subsequent dissolution. The rate of loss or gain of Ca and P into the solutions will be assessed by analysis using AA and spectrophotometry during the exposures. The effect of cariostatic ions such as Sr and F will be measured. The gradient or concentration of Ca and P and Sr or F where involved will be determined within the layers of meshes, at different time intervals. The extent of demineralization and remineralization will be determined by microradiography. The uptake of Sr and F into the lesion and/or into the remineralized area will be determined by the analysis of successive acid etches (biopsy).